Athletic shoes are becoming more expensive each year. Top-of-the-line models of the leading manufacturers can now sell for more than one hundred dollars a pair. The likelihood is that shoes will continue to become even more expensive in the years ahead as technology and performance continue to improve.
Fortunately, improvements in some features have accompanied the cost increases. Wear spots on the shoe upper have been reinforced with leather. Stitching is better and seldom unravels. Glues and molding techniques are improved, meaning that the soles are less prone to separate during use. Padding around the ankle collar and on the tongue has improved comfort. Natural and man-made fabrics are more durable and stretchproof. New elastomer components have been employed for improved heel support and eyelet strength. Replaceable insoles mold to the shape of the foot for added comfort. Heel-cushioning methods have received great attention from manufacturers and, aside from improving comfort, have reduced the risk of injury.
One area, however, in which technology has not kept pace is tread wear. For example, the tread of a good pair of running shoes manufactured in 1993 does not appear to be any more durable than the tread on a good pair manufactured in 1983, or for that matter 1973. A user rarely has a choice of running surfaces, and asphalt and other abrasive surfaces take a tremendous toll on the outersole of running shoes. The problem is exacerbated by the fact that the most pronounced tread wear, on running shoes in particular, occurs principally in two places: the outer periphery of the heel, and the ball of the foot. Heel wear is by far the more acute problem. This is understandable inasmuch as the impact force on the heel of a jogger, for example, has been estimated at about three to four times the weight of the jogger. Thus, a jogger weighing 150 pounds would create a force of 600 pounds of shock on one heel. With each heel impacting the ground approximately 800 times per mile, it is not difficult to understand why the heel of a running shoe is the first part of the shoe to wear out. The fact that this is where support is most needed only serves to compound the problem. Sadly, technological advancements in heel and midsole cushioning and construction largely can be negated by two months of heel wear.
Tread wear on other types of athletic shoes is also a problem. Basketball shoes, cross-trainers, walking and tennis shoes are other examples of athletic shoes which exhibit rapid tread wear in isolated areas or in distinctive patterns.
There appears no product on the horizon that will appreciably enhance the usable life of an athletic shoe's outersole when subjected to the usual abrasive forces. Nor do there appear to be any athletic shoes currently in the marketplace with replaceable soles or replaceable tread elements.
Designs are known that specify the replacement of the entire outersole of a shoe. Examples include those disclosed in U.S. Pat. Nos. 4,745,693 4,377,042 and 4,267,650. These concepts are impractical for most applications, especially athletic shoes, for several reasons. First, tight adherence between the sole and the shoe is difficult to achieve, particularly around the periphery of the sole. Second, replacement of the entire sole is unnecessary based upon typical wear patterns in athletic shoes. Third, replacing an entire sole is or would be more expensive than replacing simply the worn elements, a factor which is compounded if a replaceable, full-length sole for every men's and women's shoe size is to be produced. Finally, it would appear that the heel section, in particular, has entirely different needs and requirements from the rest of the shoe sole, and it deteriorates at a much faster rate.
U.S. Pat. No. 4,262,434 (Michelotti) discloses a sole for running shoes that employs detachable tread elements. However, the design of the replaceable cleats of Michelotti is impractical in many respects. For example, the cleats of Michelotti operate as the male mating elements, with the engaging post and knobs of the cleats pointing upward toward the bottom of the user's foot. This creates an insoluble dilemma. Either the female receptors are formed within a "relatively thick body 14" of the sole, which adds unnecessary thickness, weight and diminished flexibility to both the outersole and midsole in order to house the receptor space for the knob of the cleats; or the protrusion of the cleat knob makes it more likely that the user will feel the cleat knobs on the bottom of his feet, particularly after inevitable midsole deterioration that accompanies extended use. Also, the Michelotti design is simply inadequate for the heel of any athletic shoe, where detachable cleats are more prone to dislodge. The heel area requires a stronger and more durable disengagement system.